Outboard motor propeller units currently utilized for propulsion of marine craft within seawater are a danger to swimmers and aquatic animals. Such motor propeller units have therefore been replaced by pump-jet types of propulsion units having impeller blading protectively enclosed within shrouding with flow directing vanes therein for guiding impeller induced outflow of the seawater to effect marine craft propulsion. However, such pump-jet propulsion units are adversely affected by floating debris and vegetation in the seawater drawn into the flow passage enclosed by the shroud structure, causing impact damage to the impeller blading and diminishing performance of the propeller unit because of impeller flow blockage. It is therefore an important object of the present invention to render such pump-jet type of propulsion unit arrangements more advantageous as a replacement for the outboard motor propeller units, less susceptible to damage and diminished performance because of seawater debris and vegetation.